Conduits and storage/supply tanks are generally fabricated from steel and are often subjected to corrosive environments occasioned by contact of their inner surfaces with highly acidic or alkaline aqueous solutions.
Protection in such systems may be provided by lining the inside surfaces of these tanks and conduits with a resinous or cured rubber composition, which is relatively resistant to attack by such chemicals and also relatively water resistant.
In a brochure entitled “Corrosion Protection of Chemical Plant Equipment using a Bromobutyl Rubber Formula which Vulcanizes at Ambient Temperature” by C. A. Moakes and published by Polysar Corp., there is disclosed a tank or pipe lining material comprising a bromobutyl rubber formulated with curing agents (Red Lead, ethylene thiourea and a sulfur containing accelerator) which is stated to vulcanize at ambient temperature after a period of 6 or more weeks. The lining material is formulated by mixing all ingredients except the curing agents in an internal mixer, adding the curatives during a subsequent milling step and calendering the material on a roll mill to form sheets having a gauge of about 1-5 mm. These sheets are not to be stored for more than one week to avoid the risk of pre-vulcanization prior to use.
The unvulcanized sheets or liners are then applied in sections to the interior surfaces of large tanks or pipes using a primer/tie coat system to enhance adhesion of the butyl rubber sheets to metal surfaces such as steel.
The problem with this system is that it can not be stored for very long because the material may not be workable after vulcanization begins to occur, while at the same time it may take 6 weeks up to 6 months for the material to vulcanize sufficiently after application so that the material will offer the water resistant and corrosion resistant properties afforded by the cured rubber. This means that the tanks and conduits can not be used in the plant for long periods of time after they are fabricated; otherwise the lining may swell due to excess water absorption of the undervulcanized liner material.
While there are disclosures of polymers suitable for use as sealants, such as WO 99 31178; WO 00 52072; WO 00 52073; and U.S. Pat. No. 5,707,701, none have been demonstrated to be suitable for a tank liner. In particular, there has been no disclosure of a polymer suitable for a liner having a practically rapid (less than two weeks) cure time, sufficient flexibility (to allow the liner to be manipulated), and at the same time excluding curatives such as sulfur and sulfur-based accelerators that may leach into the materials being stored in the tank. What is needed is a tank liner that cures more rapidly while avoiding any leaching of materials into the materials being stored.